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Digital imaging technique measures dehydration

BioPhotonicsFeb 2007
Clinicians currently assess the presence and severity of dehydration in children using a conventional capillary-refill test and their best overall assessment of the child’s condition. A conventional test usually involves compression of the finger pulp, the nail bed or the chest wall by the examiner’s thumb or index finger for up to 5 seconds. However, current methods can be relatively inaccurate. Dr. Itai Shavit and his colleagues at the University of Calgary in Alberta, Canada, recently evaluated whether a digital videography technique could more accurately measure capillary-refill time and provide an improved assessment of dehydration.

As reported in the December issue of Pediatrics, the investigators tested 83 children with gastroenteritis by comparing the accuracy of digitally measured capillary-refill time with conventional capillary-refill testing and overall clinical assessment.

Because the gold standard for determining a child’s fluid deficit is to subtract his or her weight at initial assessment from a stable post-illness weight, the researchers also weighed the patients 48 and 72 hours after initial assessment and, if necessary, every 24 hours until their symptoms — diarrhea and vomiting — had resolved. Their fluid deficits were categorized using the World Health Organization’s definition of either no dehydration — <5% — or significant dehydration — ≥5%.

The digitally measured capillary-refill time was assessed by raising one of a child’s hands slightly above the level of the heart — from a supine position — and using a small digital video camera to film one of his or her fingertips. The camera was fixed between 3 and 5 cm from the fingertip. A researcher then lightly pressed a small smooth-tipped rod against the end of the fingertip for 5 seconds. The camera recorded the exact color characteristics of the finger both before and after compression and automatically calculated the recovery capillary-refill time.

The researchers then compared the digital videography results with those obtained by the child’s physician. The physician was asked to estimate the child’s degree of dehydration by using a 7-point Likert scale — from very mild to very severe — and to determine the capillary-refill time by using conventional techniques.

The doctors found that the sensitivity for predicting dehydration was 100 percent with the digital technique, 77 percent with the overall clinical assessment and 54 percent with the conventional method. The specificity was 91 percent, 81 percent and 88 percent, respectively. The positive likelihood ratios (for dehydration) were 11.7, 4.1 and 4.5, respectively.

The researchers believe their results indicate that digitally measured capillary-refill time more accurately predicts significant dehydration in young children with gastroenteritis than do current methods.